Signal coupling device

ABSTRACT

A signal coupling device includes a light-emitting element configured to emit light, a first element to drive the light-emitting element to output an optical signal, and a second element to receive the optical signal from the light-emitting element and to convert the optical signal into an electrical signal. A first silicone gel covers the first semiconductor element. A second silicone gel covers the second semiconductor element. A third silicone gel covers the light-emitting element. The light-emitting element, the first semiconductor element, and the second semiconductor element are encapsulated in resin material, which contacts the first, second, and third silicone gels. The first silicone gel, the second silicone gel, the third silicone gel, and the first resin material, and the resin material are transparent to light emitted by the light-emitting element. The first, second, and third silicone gels are spaced apart from each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-040633, filed Mar. 2, 2015, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a signal couplingdevice such as, for example, an optical coupling device.

BACKGROUND

An optical coupling device generates or receives an optical signalcorresponding to a voltage (or current) signal from a transmission chip.The voltage (or current) signal is used for driving light-emission of alight-emitting element, and the optical signal thus generated issubsequently received by a reception chip. The reception chip convertsthe optical signal into a voltage (or a current) signal. Opticalcoupling devices are often used as a circuit for driving a semiconductorelement, such as an insulated-gate bipolar transistor (IGBT), that isused for electric power operations. In some applications, an insulatingsignal coupling device using capacitive coupling or magnetic couplingmay be used instead of an optical coupling device.

The optical coupling device can be an integrated circuit (IC) includingthe transmission chip, the light-emitting element, and the receptionchip in one package.

The signal coupling devices may be used under various operating and/orenvironmental conditions, and thus it is desired for circuitcharacteristics such as a gain not to vary with changes in operating orenvironmental conditions.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external appearance view of an IC package of an opticalcoupling device.

FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1.

FIG. 3 is a block diagram illustrating an inner configuration of atransmission chip and a reception chip.

FIG. 4 is a cross-sectional view of the IC package of an opticalcoupling device according to a comparative example.

FIG. 5 is a graph illustrating a relationship between the thickness offirst and second encapsulating resins and a gain variation amount.

FIG. 6 is a graph illustrating a relationship between the thickness ofthe first and second encapsulating resins and a gain variation rate.

FIG. 7 is a graph illustrating a relationship between the thickness ofthe first and second encapsulating resins and the gain variation amount.

FIG. 8 is a cross-sectional view of an IC package of an optical couplingdevice according to a second embodiment.

FIG. 9 is a cross-sectional view of an IC package according to acomparative embodiment.

FIG. 10A is a cross-sectional view of a signal coupling device using amagnetic coupling or capacitive coupling.

FIG. 10B is a cross-sectional view of the signal coupling device usingthe magnetic coupling or the capacitive coupling.

DETAILED DESCRIPTION

According to a first example embodiment, a signal coupling deviceincludes a light-emitting element disposed on a first frame portion andconfigured to emit light, a first semiconductor element disposed on asecond frame portion and configured to drive the light-emitting elementto output an optical signal, and a second semiconductor element disposedon a third frame portion and configured to receive the optical signalfrom the light-emitting element and to convert the optical signal intoan electrical signal. A first silicone gel is disposed on the secondframe portion and covers the first semiconductor element. A secondsilicone gel is disposed on the third frame portion and covers thesecond semiconductor element. A third silicone gel is disposed on thefirst frame portion and covers the light-emitting element. A first resinmaterial encapsulates the light-emitting element, the firstsemiconductor element, and the second semiconductor element. The firstresin material is in contact with the first, second, and third siliconegels. In some embodiments, each of the first silicone gel, the secondsilicone gel, the third silicone gel, and the first resin material aretransparent to a wavelength of light emitted by the light-emittingelement. In some embodiments, the first, second, and third silicone gelsdo not contact each other—that is, they are spaced apart from eachother.

In general, according to a second exemplary embodiment, a signalcoupling device includes a light-emitting element that emits an opticalsignal, a first semiconductor element that drives the light-emittingelement to generate the optical signal, a second semiconductor elementthat receives the optical signal to convert the optical signal into anelectrical signal, a first silicone material of a gel type that covers aside surface and a top surface of the first semiconductor element, asecond silicone material that is disposed with being spaced away fromthe first silicone material, and covers a side surface and a top surfaceof the second semiconductor element, a third silicone material that isdisposed with being spaced away from the first and second siliconematerials, and covers a side surface and a top surface of thelight-emitting element that faces the second semiconductor element, afirst resin material that covers peripheries of the first siliconematerial, the second silicone material, and the third silicone material,a second resin material that covers periphery of the first resinmaterial. The first to third silicone materials, and the first resinmaterial are transparent with respect to a wavelength of the opticalsignal emitted from the light-emitting element, and the second resinmaterial is opaque with respect to the wavelength of the optical signalemitted from the light-emitting element.

Hereinafter, exemplary embodiments will be described with reference tothe accompanying drawings. In the following exemplary embodiments,although description will be mainly given based on specificconfigurations and operations in an optical coupling device and aninsulating device, the optical coupling device and the insulating devicemay have configurational and/or operational feature variations which arenot explicitly mentioned in the following description, which focuses onthe differences in the embodiments. Those configurations and operationsvariations which are not explicitly mentioned yet apparent to those ofordinary skill in the art are also included in the exemplaryembodiments.

FIG. 1 shows external views of an IC package 2 for an optical couplingdevice 1, and FIG. 2 is a cross-sectional view taken along line A-A inFIG. 1. As illustrated in FIG. 2, the optical coupling device 1 in FIG.1 includes a transmission chip 3, a light-emitting element 4, and areception chip 5.

For example, as illustrated in FIG. 1, the IC package 2 includes twogroups of four terminals 2 a disposed respectively along each of twoopposite sides of the IC package 2. The four terminals 2 a on one sideare connected to the transmission chip 3, and the four terminals 2 a onthe other side are connected to the reception chip 5. In the followingdescription, each of the terminals 2 a which are connected to thetransmission chip 3 is referred to as a terminal for a transmissionchip, and each of the terminals 2 a which are connected to the receptionchip 5 is referred to as a terminal for a reception chip.

A shape of the IC package 2, the number of the terminals 2 a, anddisposition of the terminal 2 a are illustrative only, and embodimentsmay vary the shape of the IC package 2 (e.g., the overhead planar shapeis not limited to rectangular), the number of terminals 2 a may bevaried (e.g., not limited to eight total terminals, and may be more orless than eight), the positioning of the terminals 2 a on IC package 2may be varied, and the number of terminals 2 a connected to receptionchip 5 may be, but is not required to be, equal to the number ofterminals 2 a connected to the transmission chip 3. FIG. 1 is exemplaryand there is no limitation of possible embodiments to the specificembodiment depicted in FIG. 1. For example, the IC package 2 accordingto this exemplary embodiment may be a surface mounting type such as SOP(small outline package), or may be an insertion mounting type such asDIP (dual in-line package). In addition, a multi-channel configurationis also possible.

As illustrated in FIG. 2, a first frame 11 on which a transmission chip(first semiconductor element) 3 and a light-emitting element (secondsemiconductor element) 4 are mounted, and a second frame 12 on which areception chip 5 is mounted are disposed to face each other inside ofthe IC package 2. More specifically, the light-emitting element 4 and alight-receiving element of the reception chip 5 are disposed to faceeach other. The transmission chip 3 and the terminal for a transmissionchip are connected to each other by a bonding wire (not specificallyillustrated), and the transmission chip 3 and the light-emitting element4 are connected to each other by a bonding wire (not specificallyillustrated). Similarly, the reception chip 5 and the terminal for areception chip are connected to each other by a bonding wire (notspecifically illustrated).

In addition, a symmetric structure, which is rotated by 180° about thecenter of the IC package 2 with the transmission chip 3 and thereception chip 5 set to face each other, is also possible. In addition,in FIG. 2, an example of mounting one transmission chip 3, onelight-emitting element 4, and one reception chip 5 in the IC package 2is illustrated, but a plurality of chips of the above-described elementsmay be respectively mounted to achieve a multi-channel configuration. Inthis case, it is preferable to maintain a relative positionalrelationship between the transmission chips 3 and the reception chips 5.

In addition, first to third encapsulating resins (first to thirdsilicone materials) 13 to 15, an inner resin (first resin material) 16,and an outer resin (second resin material) 17 are provided at the insideof the IC package 2.

The first encapsulating resin 13 covers a side surface and a top surfaceof the transmission chip 3. The second encapsulating resin 14 covers aside surface and a top surface of the reception chip 5. The thirdencapsulating resin 15 covers a side surface and a top surface of thelight-emitting element 4. The inner resin 16 covers the periphery of thefirst to third encapsulating resins 13 to 15, and the first and secondframes 11 and 12. The outer resin 17 covers the periphery of the innerresin 16. In addition, the encapsulating resins 13 to 15 may cover onlythe top surface of the respective chips. The outer resin 17 is amaterial that exists on an outer surface of the IC package 2. The firstto third encapsulating resins 13 to 15 and the inner resin 16 aretransparent resins, and more specifically, resin materials transparentwith respect to a wavelength of an optical signal emitted from thelight-emitting element 4. The outer resin 17 is a resin material opaquewith respect to the wavelength of the optical signal emitted from thelight-emitting element 4. In addition, the outer resin 17 also shieldsexternal light so that the external light does not enter thetransmission chip 3, the light-emitting element 4, and the receptionchip 5. For example, the color of the outer resin 17 is black or white.

A transmittance of the encapsulating resins 13 to 15 with respect towavelength bands of the optical signal is 90% or greater. On the otherhand, particulates of SiO₂ or the like are added to the inner resin 16to obtain a linear expansion coefficient that matches the outer resin 17as much as possible. Accordingly, a transmittance of the inner resin 16with respect to the wavelength bands of the optical signal is at leastsubstantially 40% or greater. The transmittance also depends on thethickness of a resin, and thus an absorption coefficient is 700 m⁻¹ orless.

As described above, the IC package 2 in FIG. 2 has a double-moldstructure in which an outer surface of the inner resin 16 is coveredwith the outer resin 17.

The first to third encapsulating resins 13 to 15 are disposed to bespaced from each other, and the inner resin 16 is disposed between theencapsulating resins 13 to 15 in a close contact manner. On apropagation path of the optical signal emitted from the light-emittingelement 4, the third encapsulating resin 15 that covers thelight-emitting element 4, the inner resin 16, and the secondencapsulating resin 14 that covers the reception chip 5 are present. Theresins 14, 15, and 16 are at least partially transparent, and thus theoptical signal is received by the reception chip 5 in a designed rangewithout a substantial loss.

The first to third encapsulating resins 13 to 15 are formed of asilicone gel that is softer than silicone rubber. The inner resin 16 isformed of, for example, an epoxy resin or a harden silicone rubber inwhich transparent filler or the like is mixed, and the outer resin 17 isformed of an epoxy resin in which fine carbon (e.g., carbon black),titanium dioxide (TiO₂), or the like is mixed.

FIG. 3 is a block diagram illustrating an inner configuration of thetransmission chip 3 and the reception chip 5. The transmission chip 3 inFIG. 3 includes a first reference voltage regulator 21, a firstreference voltage generating circuit 22, an A/D converter 23, a firstclock generator 24, a second clock generator 25, a modulator 26, and adriver circuit 27.

The first reference voltage generating circuit 22 generates a firstreference voltage that is used by the A/D converter 23. The firstreference voltage generating circuit 22 includes a band-gap circuit anda buffer circuit, which are not specifically illustrated. The buffercircuit buffers the first reference voltage that is generated by theband-gap circuit. The first reference voltage regulator 21 adjusts(regulates) a voltage level of the first reference voltage that isgenerated by the first reference voltage generating circuit 22.

The A/D converter 23 converts a voltage signal input to the transmissionchip 3 into a digital signal by using the first reference voltage insynchronization with a first clock signal that is generated by the firstclock generator 24 or, alternatively, a first clock signal that is inputfrom the outside. For example, the A/D converter 23 performs A/Dconversion through ΔΣ (delta-sigma) modulation, but may use other A/Dconversion methods.

The modulator 26 generates a modulation signal (for example, apulse-width-modulation (PWM) signal) based on the digital signal that isgenerated by the A/D converter 23 in synchronization with a second clocksignal that is generated by the second clock generator 25. The drivercircuit 27 controls a cathode voltage of the light-emitting element 4based on the modulation signal (for example, the PWM signal). A powersupply voltage is supplied to an anode of the light-emitting element 4.Accordingly, a voltage between the anode and the cathode of thelight-emitting element 4 varies in accordance with the modulation signal(for example, a pulse width of the PWM signal), and the light-emittingelement 4 emits an optical signal in accordance with the modulationsignal (for example, the PWM signal). For example, the light-emittingelement 4 is an LED, and emits an optical signal with intensity inaccordance with the voltage between the anode and the cathode.

The reception chip 5 includes a photo-diode 31, a transimpedanceamplifier (TIA) 32, a clock reproducing circuit 33, a demodulator (forexample, a PWM demodulator) 34, a second reference voltage generatingcircuit 35, a second reference voltage regulator 36, a D/A converter 37,and a low-pass filter (LPF) 38.

The photo-diode 31 receives the optical signal that is emitted from thelight-emitting element 4, and converts the optical signal into a currentsignal. The transimpedance amplifier 32 converts the current signal,which flows through the photo-diode 31, into a voltage signal. Thedemodulator (for example, the PWM demodulator) 34 demodulates thevoltage signal that is generated by the transimpedance amplifier 32 intoan original modulation signal (for example, a PWM modulation signal).The D/A converter 37 converts the demodulation signal that isdemodulated by the demodulator (for example, the PWM demodulator) 34into an analog voltage signal. The low-pass filter 38 outputs an analogvoltage signal after removing a low-frequency noise included in thevoltage signal that is generated by the D/A converter 37. As is the casewith the first reference voltage generating circuit 22, the secondreference voltage generating circuit 35 includes a band-gap circuit anda buffer circuit. In addition, in a case of a digital output, the D/Aconverter 37 and the low-pass filter 38 can be stopped or bypassed, anda digital signal of the clock reproducing circuit 33 and the demodulator(for example, the PWM demodulator) 34 can be directly output.

In the optical coupling devices according to the related art, even in acase of covering the reception chip 5 or the light-emitting element 4with an encapsulating member, the transmission chip 3 is not coveredwith the encapsulating member. The reason for this is as follows. Thelight-emitting element 4 and the reception chip 5 transmit and receivean optical signal to and from each other, and are required to beprotected for prevention of adherence of dust and the like, or forprevention of deterioration of the light-emitting element 4 due to astress from the inner resin 16. However, the transmission chip 3 doesnot have such a concern, and thus it is considered that the transmissionchip 3 may be directly covered with the inner resin 16 or the outerresin 17. In addition, in the related art, as a material of anencapsulating member, a material such as a silicone rubber with highhardness is used so as to prevent the encapsulating resin from beingdeformed during molding of the inner resin 16 or the outer resin 17.

In a case where the IC package of the optical coupling device accordingto the related art has a double-mold structure, in general, thereception chip and the light-emitting element are covered with anencapsulating member formed of a silicone resin of a rubber type withhigh hardness, and after covering the periphery of the encapsulatingmember and the transmission chip with a transparent resin material, theperiphery is further covered with a black resin material.

FIG. 4 is a cross-sectional view of an IC package 2 of an opticalcoupling device 1 according to a comparative example. Thecross-sectional direction in FIG. 4 is the same as in FIG. 2. The ICpackage 2 in FIG. 4 has a double-mold structure, the transmission chip 3is not covered with an encapsulating member, and the reception chip 5and the light-emitting element 4 are covered with encapsulating resins14 a and 15 a formed of a silicone rubber. The inner resin 16 is anepoxy resin or a silicone resin of a rubber-type, and the outer resin 17is an epoxy resin.

A high-temperature saturated water vapor pressure test called a“pressure cooker test” (PCT) was performed on the optical couplingdevice 1 according to the comparative example in FIG. 4 for 96 hours.From the PCT test, it may be seen that a gain that is an output voltagewith respect to an input voltage of the optical coupling device 1according to the comparative example in FIG. 4 varies. The PCT is anaccelerated life test that is performed to evaluate temperatureresistance and humidity resistance of an IC. As the cause of variationin the gain, various causes are considered. A signal level is mostlikely to vary in an operational amplifier that is used in the first andsecond reference voltage generating circuits 22 and 35 among circuitsthat configure the optical coupling device 1. Although the first andsecond reference voltage generating circuits 22 and 35 have a band-gapcircuit, an output signal of the band-gap circuit is subjected tonegative feedback control by the operational amplifier. When forming theoperational amplifier as an integrated circuit, a CMOS circuit is used.However, a differential MOS transistor pair at an input stage of theoperational amplifier is particularly susceptible to a variation inenvironmental conditions, and thus electrical characteristics thereoftend to vary.

It is known that a channel mobility of the MOS transistors varies inaccordance with a stress. When the IC in FIG. 1 is placed in thehigh-temperature and high-humidity atmosphere (e.g., undergoes PCT),volume expansion occurs in resins inside the IC package 2, and when acompressive stress due to this volume expansion is applied to thetransmission chip 3 and the reception chip 5 during device operation,the electrical characteristics of the differential MOS transistor pairin the operational amplifier unevenly varies. Accordingly, there is aconcern that an off-set voltage may occur in the operational amplifier.When the off-set voltage occurs in the operational amplifier, a voltagelevel of a reference voltage varies, and thus a level of a signal thatis output from the transmission chip 3 or the reception chip 5 varies.As a result, it is considered that the gain of the optical couplingdevice 1 also varies.

As described above, the first or second reference voltage generatingcircuit 22 or 35, which include an operational amplifier, is included inthe transmission chip 3 and the reception chip 5, and thus a variationin the reference voltage due to stress tends to occur in both of thechips. In addition, when a difference occurs between stresses applied tothe respective chips (chip 3 and chip 5), an amount of variation in thereference voltage is not uniform and may be different in each case.Accordingly, when operated under severe conditions for a long period oftime, there is a concern that a gain variation of the optical couplingdevice 1 increases.

In addition, an operational amplifier, which is used in the first andsecond reference voltage generating circuits 22 and 35, is also used forcontrol other than the negative feedback control of the band-gapcircuit. The reference voltage that is generated by a band-gap circuitis input to a buffer circuit, but an operational amplifier is also usedin the buffer circuit.

As described above, the first or second reference voltage generatingcircuit 22 or 35 may include a plurality of the operational amplifiers.If the off-set voltage varies in accordance with applied stresses on thevarious operational amplifier occurs, an amount of variation in eachoff-set voltage will generally not be uniform, and a relative balancebetween these various operational amplifiers collapses, it may thus beconsidered that the gain of the optical coupling device 1 greatly variesunder long-term operating conditions.

From experimental results it has been found that when the transmissionchip 3 and the reception chip 5 are covered with an encapsulating memberformed of a silicone gel, it is possible to mitigate a stress. Thesilicone gel has a hardness value less than that of an epoxy resin or asilicone rubber, and thus the silicone gel is a material that tends toplastically deform more easily than these other materials. The hardnessvalue of the silicone gel may be measured, for example, by a durometer.For the silicone gel that is used in this example embodiment, thehardness value, which is measured by the durometer in accordance withJapanese Industrial Standards (JIS) K 6253 or JIS K 7215 (Type A), is ina range of 10 to 24, for example, 16 to 24. An experiment was carriedout varying the hardness value of the applied silicone gel material.From experiment, it may be seen that if the hardness value is less than10, the shape of the silicone gel tends to collapse (deform), and thusthere is a concern that it is difficult to stably maintain an intendedexternal shape of the first to third encapsulating resins 13 to 15 whensuch material is used. In addition, it may be seen that if the hardnessvalue is 16 or greater, it is possible to form a more stable shape. Inaddition, it may be seen that if the hardness value exceeds 24, theadhesiveness between such a gel and the inner resin 16 may deteriorate,and a gap between the materials may form. If the gap occurs, there is aconcern that peeling-off may occur or an insulation withstand voltageperformance may deteriorate, and thus the presence of a gap is notpreferable. In addition, the interface between the materials (theencapsulating resin and the inner resin) may include a peeled-offportion and a still-adhered or a still-in-contact portion; however, thestate of the interface will vary with time (e.g., additional portionsmay peel off and/or peeled-off portions may be brought back intocontact) under long-term operating conditions and thus devicecharacteristics may vary with time in an unpredictable manner. At aninterface between different resin materials, amounts of deformation canbe different between a longitudinal direction and a lateral direction,the amount of deformation is generally greater in the longitudinaldirection, and the amount of deformation is generally less in thelateral direction. Accordingly, there is a tendency for expansion of theencapsulating resin to most obviously occur at the apex portion (in avertical direction) of the resin body, and for shrinkage of theencapsulating resin to most obviously occur at a peripheral portion (ina horizontal direction).

For reference, hardness value of the inner resin 16, as measured by adurometer (in accordance with the same above-listed standards), is 75.When the hardness of a silicone resin of a gel type is in a range of 10to 24, the adhesiveness between the first to third encapsulating resins13 to 15 and the inner resin 16 (having hardness approximately 75) isgenerally satisfactory, and peeling-off does not occur before or afterthe accelerated life testing, such as PCT, and interfacial peeling isnot found at the apex portion or the peripheral portion of theencapsulating resins 13 to 15. As described above, it is preferable thatthe hardness value of the inner resin 16 be three or more times thehardness value of the first to third encapsulating resins 13 to 15.

If the transmission chip 3, the reception chip 5, and the light-emittingelement 4 are covered with the silicone gel with a hardness value of 10to 24, and preferably 16 to 24, even when carrying out the acceleratedlife test (such as PCT) under the high-temperature and high-humidity, itis possible to mitigate stresses which affect the transmission chip 3and the reception chip 5, and thus it is possible to suppress thevariation in gain, which is exhibited as an output voltage/an inputvoltage of the optical coupling device 1, to a certain extent with noproblem in practical use.

In the related art, as illustrated in the comparative example of FIG. 4,in a case of double-molding an isolation IC, the reception chip 5 andthe light-emitting element 4 are covered with encapsulating resins 14 aand 15 a which are formed of a relatively hard (i.e., greater hardnessthan the silicone gel type materials used as encapsulating resins 13 to15) resin material such as a silicone rubber. And with respect to thetransmission chip 3, an encapsulating member is not formed and the innerresin 16 is formed directly contacting the side and upper surfaces ofthe transmission chip 3. The outer resin 17 is formed in a similarmanner as is depicted in FIG. 2. The adhesiveness between the innerresin 16 and the encapsulating resins 14 a and 15 a deteriorates, andthus interfacial peeling-off tends to occur particularly near a sidesurface portion of the reception chip 5. On the other hand, on an uppersurface side of the reception chip 5, the encapsulating resins 14 a and15 a and the inner resin 16 are strongly bonded to each other.Accordingly, when the accelerated life test is performed, a stress tendsto be applied to the upper surface side of the reception chip 5, whichtends to cause variation in gain to occur. In addition, the side surfaceand the top surface of the transmission chip 3 is directly covered withthe inner resin 16, and the inner resin 16 is also a hard material, andthus there is a concern that a stress may also be applied to thetransmission chip 3. Additionally, the amount of deformation of theresin at the periphery of the reception chip 5 and the transmission chip3 is not uniform before and after long-term operation, and thus there isa possibility that operational balance of components may be lost.

In contrast, in the embodiment depicted in FIG. 2, both of thetransmission chip 3 and the reception chip 5 are covered with the firstand second encapsulating resins 13 and 14, both of which are formed of asoft silicone gel (hardness range 10 to 24). Accordingly, the stress maybe dispersed in this silicone gel type material, and thus even whenperforming PCT under high-temperature and high-humidity conditions, itis possible to reduce the stress that is applied to the transmissionchip 3 and the reception chip 5 while maintaining operational balancebetween component. In addition, stress is not strongly applied to a partof the surface of the transmission chip 3 and the reception chip 5because the first to third encapsulating resins 13 to 15 are formed ofthe silicone gel type material, and thus adhesiveness with the innerresin 16 is also satisfactory, and partial peeling-off does not occur.

As demonstrated by experiment, even when using the silicone gel asdescribed above, if the thickness of the first and second encapsulatingresins 13 and 14 are altered, it may be seen that the gain variationamount will still greatly vary. That is, it is necessary to select anappropriate thickness for the first and second encapsulating resins 13and 14 formed of silicone gel type material.

FIG. 5 is a graph illustrating measured gain variation amount during PCTfor different thicknesses for first encapsulating resin 13 and secondencapsulating resin 14. In FIG. 5 each graph (G1-G8) illustratesmeasurement results of the gain variation amount with the passage oftime for four optical coupling devices 1 (hereinafter, referred to as aspecimen) for eight different cases including cases where at least oneof the first and second encapsulating resins 13 and 14 is not present(i.e., zero thickness) (see G1, G2, G4), a case where the firstencapsulating resin 13 has a small thickness (120 μm to 170 μm) (seeG3), cases where the first encapsulating resin 13 has a medium thickness(170 μm to 220 μm) (see G4, G5, G6, G7, and a case where the firstthickness is great (220 μm to 270 μm). In respective graphs, thehorizontal axis represents a test time during the PCT, and the verticalaxis represents the gain variation amount. A graph G1 represents a casewhere the transmission chip 3 and the reception chip 5 are not coveredwith the first and second encapsulating resins 13 and 14, a graph G2represents a case where only the reception chip 5 is covered with thesecond encapsulating resin 14, a graph G3 represents a case where thethickness of the first encapsulating resin 13 is small, and thethickness of the second encapsulating resin 14 is medium, a graph G4 toa graph G7 represent a case where the thickness of the firstencapsulating resin 13 is medium, and the thickness of the secondencapsulating resin 14 is zero, small, medium, and large, and a graph G8represents a case where the thickness of the first encapsulating resin13 is great, and the thickness of the second encapsulating resin 14 ismedium. The four lines in the graphs G1 to G8 represent measurementresults of four specimens in each test.

As may be seen from the graphs G1 to G8, if the thickness of the firstand second encapsulating resins 13 and 14 is medium or greater, the gainvariation amount is less. In addition, it may be seen that the greaterthe thickness of the first and second encapsulating resins 13 and 14,the greater the effect in reducing the gain variation amount is.

FIG. 6 is a diagram illustrating a gain variation rate with respect tothe thickness of the first encapsulating resin 13 and the secondencapsulating resin 14 (a gain variate after 96 h/an initial value). InFIG. 6, the horizontal axis represents the thickness of the firstencapsulating resin 13, and the vertical axis represents the thicknessof the second encapsulating resin 14.

In FIG. 6, a region r1 represents a region in which a ratio of thethickness of the second encapsulating resin 14 to the thickness of thefirst encapsulating resin 13 is significantly large, a region r2represents a region in which the above-described ratio is large next tothe region r1, a region r3 is a region in which the above-describedratio is large next to the region r2, a region r4 is a region in whichthe above-described ratio is large next to the region r3, and a regionr5 is a region in which the above-described ratio is large next to theregion r4. In addition, a region r6 is a region in which the ratio ofthe thickness of first encapsulating resin 13 to the thickness of thesecond encapsulating resin 14 is significantly large, a region r7 is aregion in which the above-described ratio is large next to the regionr6, a region r8 is a region in which the above-described ratio is largenext to the region r7, a region r9 is a region in which theabove-described ratio is large next to the region r8, and a region r10is a region in which the above-described ratio is large next to theregion r9.

In the regions r1 to r5, a gain variation rate toward a negativedirection increases. Here, the negative direction represents that a gainbecomes smaller than the original gain. Particularly, in the regions r1and r2 (the thickness of the second encapsulating resin 14 is 180 μm orgreater, and the thickness of the first encapsulating resin 13 is 100 μmor less), the negative gain variation rate further increases.

On the other hand, the regions r6 to r9 are regions in which thethickness of the first encapsulating resin 13 is greater than thethickness of the second encapsulating resin 14, and in these regions r6and r9, the gain variation rate toward a positive direction increases.Here, the positive direction represents that a gain becomes larger thanthe original gain. Particularly, in the regions r6 and r7 (the thicknessof the first encapsulating resin 13 is 180 μm or greater, and thethickness of the second encapsulating resin 14 is 100 μm or less), thepositive gain variation rate further increases. In a region r10 betweenthe regions r1 to r4 and the regions r6 to r9, the gain variation rateis the smallest. The region r10 is a region in which the thickness of afirst encapsulating member and the thickness of a second encapsulatingmember are substantially the same. In addition, if the thickness of thefirst encapsulating member and the thickness of the second encapsulatingmember are 200 μm or greater, it may be seen that even when a differenceoccurs in the thickness of both of the encapsulating members, thevariation amount is small.

FIG. 7 is a diagram illustrating a gain variation amount (a differencebetween a gain value after 96 h and an initial gain value) with respectto the thickness of the first encapsulating resin 13 and the secondencapsulating resin 14. In FIG. 7, the horizontal axis represents thethickness of the first encapsulating resin 13, and the vertical axisrepresents the thickness of the second encapsulating resin 14.

In FIG. 7, a region r11 represents a region in which a ratio of thethickness of the second encapsulating resin 14 to the thickness of thefirst encapsulating resin 13 is significantly large, a region r12 is aregion in which the above-described ratio is large next to the regionr11, a region r13 is a region in which the above-described ratio islarge next to the region r12, a region r14 is a region in which theabove-described ratio is large next to the region r13, and a region r15is a region in which the above-described ratio is large next to theregion r14. In addition, a region r16 is a region in which a ratio ofthe thickness of the first encapsulating resin 13 to the thickness ofthe second encapsulating resin 14 is significantly large, a region r17is a region in which the above-described ratio is large next to theregion r16, a region r18 is a region in which the above-described ratiois large next to the region r17, a region r19 is a region in which theabove-described ratio is large next to the region r18, and a region r20is a region in which the above-described ratio is large next to theregion r19.

In the regions r11 to r15, the gain variation amount toward the negativedirection increases, and in the regions r16 to r19, the gain variationamount toward the positive direction increases. In the region r20between the regions r11 to r15, and the regions r16 to r19, the gainvariation amount is the smallest. The region r20 is a region in whichthe thickness of the first encapsulating member and the thickness of thesecond encapsulating member are substantially the same. In addition, ifthe thickness of the first encapsulating member and the thickness of thesecond encapsulating member are 200 μm or greater, it may be seen thateven when a difference occurs in the thickness of both of theencapsulating members, the variation amount is small.

That is, as may be seen from the diagrams in FIGS. 6 and 7, it ispreferable that the thickness of the first and second encapsulatingmember are made to be equal to each other, and are set as approximately100 μm to 250 μm. In addition, when the thickness on one side is 200 μmor greater, it is preferable to set the thickness of the first andsecond encapsulating members greater than 200 μm.

As described above, in the case of the double-mold structure, a greatdifference occurs in the thickness of the first encapsulating resin 13and the second encapsulating resin 14, a difference also occurs in thestress which is applied to the transmission chip 3 and the receptionchip 5, and thus the gain variation amount increases. Accordingly, it ispreferable that the first encapsulating resin 13 and the secondencapsulating resin 14 are set to have substantially the same thickness.As will be described later, it is necessary to change the thickness ofthe first and second encapsulating resins 13 and 14 due to the thicknessor the area of the transmission chip 3 or the reception chip 5, and thelike. Accordingly, more specifically, it is preferable to optimize thethickness of the first and second encapsulating resins 13 and 14 suchthat a stress applied to the transmission chip 3 and a stress applied tothe reception chip 5 are substantially equal to each other, and stressvalues decrease.

In addition, from FIG. 7, it may be seen that as the thickness of thefirst and second encapsulating resins 13 and 14 increases, a region inwhich the gain variation amount decreases exists.

When referring to FIG. 7, it may be seen that the lower limit of thethickness of the first and second encapsulating resins 13 and 14 is 100μm or greater, preferably 200 μm or greater, and more preferably 250 μmor greater.

In addition, the upper limit of the thickness of the first and secondencapsulating resins 13 and 14 is set to satisfy a condition in whichthe first encapsulating resin 13, the second encapsulating resin 14, andthe third encapsulating resin 15 that covers the side surface and thetop surface of the light-emitting element 4 do not come into contactwith each other. The reason for this is because if the first to thirdencapsulating resins 13 to 15 come into contact with each other, thereis a concern that insulation withstand voltage may decrease.

In addition, in the international safety standard (VDE: Verband DeutsherElectrotechnisher) of a photo-coupler and the like, a withstand voltageof 3.75 kV is required at a space insulation distance of 0.4 mm betweenthe transmission chip 3 and the reception chip 5. According to thestandard, it is necessary to secure an insulation distance of 0.2 mm inrespective conductive regions including a wire on a transmission chip 3side and a wire on a reception chip 5 side. That is, it is necessary forthe space insulation distance to be 0.4 mm or greater. A bonding wire isconnected to the top surface of the transmission chip 3 and thereception chip 5, and the thickness of the bonding wire is approximately100 μm to 200 μm. With regard to the space insulation distance that isthe closest separation distance between respective conductive portionson a transmission chip 3 side and on a reception chip 5 side, it isnecessary to secure 0.4 mm in a connection state with the bonding wire.Accordingly, so as to achieve the thinnest package, it is necessary tosuppress the upper limit of the thickness of the first and secondencapsulating resins 13 and 14, which are adjacent to or intersect eachother, to 300 μm to 400 μm.

In summary, as may be seen from the graphs in FIGS. 5 and 6, the lowerlimit of the thickness of the first and second encapsulating resins 13and 14 is 100 μm or greater, preferably 200 μm or greater, and morepreferably 250 μm or greater.

In addition, the upper limit of the thickness of the first and secondencapsulating resins 13 and 14 is set to satisfy a condition in whichthe first to third encapsulating resins 13 to 15 do not come intocontact with each other, and the upper limit is specifically 300 μm to400 μm in consideration of the international safety standard.

In addition, the thickness of the first and second encapsulating resins13 and 14 may be set to the maximum thickness in the vicinity of thecentral portion of the transmission chip 3 or the reception chip 5 whenconsidering that the thickness in the vicinity of the central portion ofeach of the chips 3 and 5 is greater than the thickness of an edgeportion. More preferably, the upper limit is an average thickness on asurface of the transmission chip 3 or the reception chip 5.

In addition, even in a symmetric structure which is rotated by 180°about the center of the package 2 with the transmission chip 3 and thereception chip 5 set to face each other, it is possible to obtainsatisfactory results. On the other hand, if one of the transmission chip3 and the reception chip 5 greatly deviates from a relative position,there is a concern that the gain variation rate before deviation may beshifted to the region r2 or r7, and the like from the region r10 in FIG.6 after deviation. Accordingly, it is necessary for a relative positionof the transmission chip 3 and the reception chip 5 to be restrictedfrom the center of symmetry within at least 15% of a dimension of a longside of the chips. The reason for the restriction is because apermissible thickness in the variation rate in FIG. 6 is 30 μm, and theminimum value in a thickness necessary for coating is 100 μm. As is thecase with a multi-channel structure and the like, if a plurality ofchips are mounted, with regard to a pair of transmission chip 3 andreception chip 5 between which a signal is exchanged, it is alsonecessary for the relative position thereof to be restricted within 15%of a dimension of a long side of the chips.

However, it is considered that the larger the thickness of thetransmission chip 3 and the reception chip 5 is, the higher theresistance against a stress becomes. Accordingly, as the thickness ofthe transmission chip 3 and the reception chip 5 increases, thethickness of the first and second encapsulating resins 13 and 14, whichis necessary for mitigation of the stress, may be decreased. It has beenseen that the thickness of the first and second encapsulating resins 13and 14, and the thickness of the transmission chip 3 and the receptionchip 5 have a substantially inversely proportional relationship. Forexample, if the thickness of the transmission chip 3 or the receptionchip 5 is set as t1, and an inversely proportional coefficient is set ask1, the lower limit of the thickness of the first or secondencapsulating resin 13 or 14, which is necessary for mitigation of astress, is equal to or greater than a range of k1×100/t1 to k1×250/t1.Similarly, the upper limit of the thickness of the first or secondencapsulating resin 13 or 14, which is required for mitigation of astress, is equal to or less than a range of k1×300/t1 to k1×400/t1.

Similarly, it is considered that the greater the thickness of the ICpackage 2 of the optical coupling device 1 is, the higher the resistanceagainst a stress becomes. Accordingly, as the thickness of the ICpackage 2 increases, the thickness of the first and second encapsulatingresins 13 and 14, which is necessary for mitigation of the stress, maybe decreased. It has been seen that the thickness of the first andsecond encapsulating resins 13 and 14 and the thickness of the ICpackage 2 have the substantially inversely proportional relationship.For example, if the thickness of the IC package 2 is set as t2, and aninversely proportional coefficient is set as k2, the lower limit of thethickness of the first or second encapsulating resin 13 or 14, which isrequired for mitigation of a stress, is equal to or greater than a rangeof k2×100/t2 to k2×250/t2. Similarly, the upper limit of the thicknessof the first or second encapsulating resin 13 or 14, which is requiredfor mitigation of a stress, is equal to or less than a range ofk2×300/t2 to k2×400/t2.

In addition, it has been seen that the stress applied to thetransmission chip 3 and the reception chip 5 also depends on the surfacearea of the transmission chip 3 and the reception chip 5. The larger thesurface area is, the more stress that tends to be applied. It has beenseen that the surface area and the stress of the transmission chip 3 andthe reception chip 5 have the substantially proportional relationship.For example, if the surface area of the transmission chip 3 or thereception chip 5 is set as t3, and a proportional coefficient is set ask3, the lower limit of the thickness of the first or secondencapsulating resin 13 or 14, which is required for mitigation of thestress, is equal to or greater than a range of k3×100×t3 to k3×250×t3.Similarly, the upper limit of the thickness of the first or secondencapsulating resin 13 or 14, which is required for mitigation of thestress, is equal to or less than a range of k3×300×t3 to k3×400×t3.

As illustrated in FIG. 2, not only the transmission chip 3 and thereception chip 5 are covered with the first and the second encapsulatingresins 13 and 14, but also the side surface and/or the top surface ofthe light-emitting element 4 is covered with the third encapsulatingresin 15. It is considered that the optical signal that is emitted fromthe light-emitting element 4 is not affected by stress, and thus thethird encapsulating resin 15 is not requisite from the viewpoint ofstress mitigation. However, as is the case with the first and secondencapsulating resins 13 and 14, it is preferable that the light-emittingelement 4 is covered with the third encapsulating resin 15 formed of asilicone gel in consideration of protection of the light-emittingelement 4, adhesiveness with the inner resin 16, and the like. Thereason for the preference is as follows. If a gap occurs at theperiphery of the light-emitting element 4 due to a variation with thepassage of time, reflection of light occurs in accordance with the gap.As a result, an amount of light varies in the reception chip 5, anddeterioration is caused due to an increase in defects inside an elementor propagation of the defects when peeling-off andpartial-stress-concentration close contact occur.

As described above, in the first embodiment, in the optical couplingdevice 1 having the double-mold structure, the transmission chip 3 andthe reception chip 5 are covered with the first and second encapsulatingresins 13 and 14, each being formed of the silicone gel, and thus evenwhen performing the accelerated life test such as the PCT in ahigh-temperature and high-humidity atmosphere, the stress applied to thetransmission chip 3 or the reception chip 5 is mitigated with thesilicone gel and becomes more uniform. Accordingly, it is possible tosuppress a gain variation of the optical coupling device 1. In addition,the thickness of the first and second encapsulating resins 13 and 14 isoptimized, and thus it is possible to minimize the gain variation of theoptical coupling device 1.

Second Embodiment

FIG. 8 is a cross-sectional view of an IC package 2 of an opticalcoupling device 1 according to a second embodiment, and FIG. 9 is across-sectional view of an IC package 2 according to a comparativeexample. The IC package 2 in FIGS. 8 and 9 has a single mold structure.

As is the case with the first embodiment, in the IC package 2 in FIG. 8,the transmission chip 3 is covered with the first encapsulating resin 13formed of silicone gel. In addition, in the IC package 2 in FIG. 8, theside surface and the top surface of the light-emitting element 4, theside surface and the top surface of the reception chip 5, and an opticalpath from the light-emitting element 4 to the light-receiving element 5are covered with a silicone rubber 18 that is harder than silicone gel.In addition, a film 19 (insulating film) is disposed at an intermediateposition between the silicone rubber portions adjacent to light-emittingelement 4 and the reception chip 5, and the silicone rubber is thusdivided into two parts by the film 19. The periphery of the siliconerubber 18 and the first encapsulating resin 13 is covered with the outerresin 17.

The film 19 is intended to prevent device short-circuiting fromoccurring during the accelerated life test such as PCT in thehigh-temperature and high-humidity atmosphere due to a gap that mightform between the silicone rubber and the outer resin 17. In addition, insome embodiments, encapsulation may be carried out with the silicone gelinstead of the silicone rubber to further raise the insulation withstandvoltage—that is, element 18 can be a silicone gel material similar tothe first encapsulating resin 13.

In the comparative example illustrated in FIG. 9, the transmission chip3 is not covered with the first encapsulating resin 13, and comes intodirect contact with the outer resin 17.

In the case of the comparative example in FIG. 9, the outer resin 17 isharder than the silicone gel or the silicone rubber, and thus the outerresin 17 does not serve to mitigate stresses applied to the transmissionchip 3, and a reference voltage in the transmission chip 3 may thusvary. As a result, there is a concern that gain variation in the opticalcoupling device 1 may occur.

In contrast, in the IC package 2 illustrated in FIG. 8, the transmissionchip 3 is covered with the first encapsulating resin 13 formed of thesilicone gel or the silicone rubber as in the first embodiment.Accordingly, even in long-term and severe conditions such as in-vehicleuse, it is possible to mitigate stresses with the silicone gel or thesilicone rubber, and thus it is possible to suppress the gain variationof the optical coupling device 1.

When referring to FIG. 6, it may be seen that if the thickness of thefirst encapsulating resin 13 exceeds approximately 200 μm, it ispossible to suppress the gain variation without depending on thethickness of a first encapsulating member on a reception chip 5 side.From FIG. 6, it may be seen that if the thickness of the firstencapsulating resin 13 is 200 μm, the gain variation slightly depends onthe thickness of the encapsulating member on the reception chip 5 side,but if the thickness exceeds 250 μm, the gain variation does not mostlydepend on the thickness of the encapsulating member on the receptionchip 5 side. Accordingly, it is desirable to set the thickness of thefirst encapsulating resin 13, which covers the transmission chip 3 inthe single mold structure, to 200 μm or greater, and more preferably 250μm or greater.

In addition, the upper limit of the thickness of the first encapsulatingresin 13 is set in a range satisfying a condition in which the firstencapsulating resin 13 does not come into contact with the siliconerubber or the silicone rubber on an adjacent reception side (e.g., theportion of material 18 adjacent to reception chip 5).

As described above, even in the case of configuring the IC package 2 ofthe optical coupling device 1 with a single mold, if the transmissionchip 3 is covered with the first encapsulating resin 13 formed of thesilicone gel or the silicone rubber similar to the first embodiment, itis possible to mitigate stresses applied to the transmission chip 3, andthus it is possible to suppress the gain variation of the opticalcoupling device 1.

Third Embodiment

In the above-described first and second embodiment, description is givenof the optical coupling device in which transmission and reception ofthe optical signal from the light-emitting element 4 are carried outwith the optical signal transmitting and optical signal receivingelements being electrically isolated/insulated from each other, butother insulating signal coupling devices may also transmit a signal in acontactless manner, for example, through magnetic coupling or capacitivecoupling.

In a case of carrying out signal transmission through the magneticcoupling, for example, a coil on a transmission chip side and a coil ona reception chip side may be disposed to be magnetically coupled.Alternatively, a resistance bridge circuit may be provided on thereception chip side in combination with provision of the coil on thetransmission chip side.

In addition, in a case of carrying out signal transmission through thecapacitive coupling, for example, a capacitor may be provided betweenthe transmission chip and the reception chip, an electrode on one sideof the capacitor may be connected to the transmission chip, and anelectrode on the other side may be connected to the reception chip.

Even in the insulating signal coupling devices that carries out thesignal transmission through the magnetic coupling or the capacitivecoupling, a reference voltage generating circuit is provided in thetransmission chip and the reception chip, and thus the reference voltagethat is generated by this reference voltage generating circuit variesdue to stress applied to the transmission chip or the reception chip.Accordingly, as described in the first and second embodiments, it isdesirable to cover the transmission chip and/or the reception chip withencapsulating resin formed of silicone gel so as to mitigate the stress.

FIGS. 10A and 10B are cross-sectional views of insulating signalcoupling devices using magnetic coupling or capacitive coupling. In thecase of FIG. 10A, the transmission chip 3 and the reception chip 4 areinsulated from each other, and a stacked body 41 of passive elementssuch as an insulated coil and a capacitor are disposed on the frame 11.Each of the transmission chip 3, the reception chip 4, and the stackedbody 41 are separately covered with encapsulating resins 13, 14, and 42,respectively, which are formed of silicone gel or silicone rubber asdiscussed in conjunction with the first embodiment.

In FIG. 10B, the transmission chip 3 and the reception chip 4 areinsulated from each other and disposed on a frame 11, and the stackedbody 41 including passive elements, such as the insulated coil and thecapacitor, is integrated with the reception chip 4. As described in thefirst and second embodiments, the side surface and the top surface ofthe transmission chip 3 and the reception chip 4 are covered with anencapsulating resin (13 and 14, respectively) formed of silicone gel orsilicone rubber.

FIGS. 10A and 10B illustrate a single mold structure, and thus it ispreferable that the thickness of the encapsulating resin 13 which coversthe transmission chip 3, and the encapsulating resin 14 which covers thereception chip 4, are set to a thickness of 200 μm or greater, assimilar to the second embodiment. In addition, with regard to theencapsulating resins (13 and 14, respectively) that cover thetransmission chip 3 and the reception chip 4, the thickness thereof isdesirable to be substantially the same at each position.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A signal coupling device, comprising: alight-emitting element disposed on a first frame portion and configuredto emit light; a first semiconductor element disposed on a second frameportion and having an operational amplifier with a CMOS circuit, thefirst semiconductor element being configured to drive the light-emittingelement to output an optical signal, the first semiconductor elementincluding a first reference voltage generating circuit configured togenerate a first reference voltage, the first semiconductor elementincluding an analog-to-digital converter configured to convert a voltagesignal into a digital signal based on the first reference voltage and amodulator configured to generate a modulation signal synchronized withthe optical signal based on the digital signal; a second semiconductorelement disposed on a third frame portion and configured to receive theoptical signal from the light-emitting element and to convert theoptical signal into an electrical signal, the second semiconductorelement including a second reference voltage generating circuitconfigured to generate a second reference voltage, the secondsemiconductor element including a photoelectric converter, thephotoelectric converter configured to convert the optical signal to theelectrical signal, a demodulator configured to demodulate the electricalsignal, and a digital-to-analog converter configured to convert theelectrical signal into an analog voltage signal based on the secondreference voltage; a first silicone gel disposed on the second frameportion and covering the first semiconductor element; a second siliconegel disposed on the third frame portion and covering the secondsemiconductor element; a third silicone gel disposed on the first frameportion and covering the light-emitting element; and a first resinmaterial encapsulating the light-emitting element, the firstsemiconductor element, and the second semiconductor element andcontacting the first, second, and third silicone gels, wherein the firstsilicone gel suppresses variations in the first reference voltage. 2.The signal coupling device according to claim 1, wherein the firstsilicone gel, the second silicone gel, the third silicone gel, and thefirst resin material are transparent to a wavelength of light emitted bythe light-emitting element, and the first, second, and third siliconegels are spaced apart from each other.
 3. The signal coupling deviceaccording to claim 1, further comprising: a second resin materialencapsulating the first resin material, wherein the second resinmaterial is substantially opaque with respect to a wavelength of lightemitted by the light-emitting element, and the first resin material istransparent to the wavelength.
 4. The signal coupling device accordingto claim 1, wherein the first silicone gel has a hardness value asdetermined in accordance with at least one of Japanese IndustrialStandard K 6253 and Japanese Industrial Standard K 7215 that is in arange from 10 to
 24. 5. The signal coupling device according to claim 4,wherein the second silicone gel has a hardness value as determined inaccordance with at least one of Japanese Industrial Standard K 6253 andJapanese Industrial Standard K 7215 that is in a range from 10 to
 24. 6.The signal coupling device according to claim 5, wherein the thirdsilicone gel has a hardness value as determined in accordance with atleast one of Japanese Industrial Standard K 6253 and Japanese IndustrialStandard K 7215 that is in a range from 10 to
 24. 7. The signal couplingdevice according to claim 4, wherein a hardness value of the first resinmaterial as determined in accordance with at least one of JapaneseIndustrial Standard K 6253 and Japanese Industrial Standard K 7215 thatis greater than the hardness value of the first silicone gel by at leasta factor of three.
 8. The signal coupling device according to claim 1,wherein the first silicone gel has a hardness value as determined inaccordance with at least one of Japanese Industrial Standard K 6253 andJapanese Industrial Standard K 7215 that is in a range of 16 to
 24. 9.The signal coupling device according to claim 1, wherein the first,second, and third silicone gels are a same material.
 10. The signalcoupling device according to claim 1, wherein an average thickness ofthe first silicone gel on a surface of the first semiconductor elementfacing away from the second frame portion and an average thickness ofthe second silicone gel on a surface of the second semiconductor elementfacing away from the third frame portion are each greater than or equalto 100 μm and less than or equal to 400 μm.
 11. The signal couplingdevice according to claim 1, further comprising: an insulating filmdisposed between the light-emitting element and the second semiconductorelement in an optical path from the light-emitting element and thesecond semiconductor element, the second silicone gel contacting a firstsurface of the insulating film, the third silicone gel contacting asecond surface of the insulating film opposite the first surface.
 12. Asignal coupling device, comprising: a light-emitting element disposed ona first frame portion and configured to emit light; a firstsemiconductor element disposed on a second frame portion and having andoperation amplifier with a CMOS circuit, the first semiconductor elementbeing configured to drive the light-emitting element to output anoptical signal, the first semiconductor element including a firstreference voltage generating circuit configured to generate a firstreference voltage, the first semiconductor element including ananalog-to-digital converter configured to convert a voltage signal intoa digital signal based on the first reference voltage and a modulatorconfigured to generate a modulation signal synchronized with the opticalsignal based on the digital signal; a second semiconductor elementdisposed on a third frame portion and configured to receive the opticalsignal from the light-emitting element and to convert the optical signalinto an electrical signal, the second semiconductor element including asecond reference voltage generating circuit configured to generate asecond reference voltage, the second semiconductor element including aphotoelectric converter, the photoelectric converter configured toconvert the optical signal to the electrical signal, a demodulatorconfigured to demodulate the electrical signal, and a digital-to-analogconverter configured to convert the electrical signal into an analogvoltage signal based on the second reference voltage; a first siliconematerial disposed on the second frame portion and covering the firstsemiconductor element, the first silicone material being a gel; a secondsilicone material disposed on the third frame portion and covering thesecond semiconductor element, the second silicone material being one ofa gel and a rubber; a third silicone material disposed on the firstframe and covering the light emitting element, the third siliconematerial being one of a gel and a rubber; and a first resin materialencapsulating the light-emitting element, the first semiconductorelement, and the second semiconductor element and contacting the first,second, third silicone materials, wherein the first silicone materialsuppresses variations in the first reference voltage.
 13. The signalcoupling device according to claim 12, wherein the second and thirdsilicone materials are transparent at a wavelength of light emitted bythe light-emitting element, and the first silicone material is spacedapart from the second and third silicone materials.
 14. The signalcoupling device according to claim 12, further comprising: an insulatingfilm disposed between the light-emitting element and the secondsemiconductor element in an optical path from the light-emitting elementand the second semiconductor element, the second silicone materialcontacting a first surface of the insulating film, the third siliconematerial contacting a second surface of the insulating film opposite thefirst surface.
 15. The signal coupling device according to claim 14,wherein the first resin material is opaque with respect to thewavelength of light emitted by the light-emitting element.
 16. Thesignal coupling device according to claim 14, wherein the second andthird silicone materials are silicone rubbers.
 17. The signal couplingdevice according to claim 12, wherein the first silicone material has ahardness value as determined in accordance with at least one of JapaneseIndustrial Standard K 6253 and Japanese Industrial Standard K 7215 thatis in a range from 10 to
 24. 18. The signal coupling device according toclaim 12, wherein an average thickness of the first silicone material ona surface of the first semiconductor element facing away from the secondframe portion is greater than or equal to 200 μm.
 19. The signalcoupling device according to claim 1, wherein the second silicone gelsuppresses variations of the second reference voltage.
 20. The signalcoupling device according to claim 12, wherein the second siliconematerial suppresses variations of the second reference voltage.